The actions of fibroblast growth factors (FGFs) are mediated via a family of four closely related FGF receptor genes (FGFRs 1-4). FGFR1, FGFR2, and FGFR4 have unique patterns of expression during embryogenesis suggesting that these receptors mediate different functions of FGFs during development. In the present study, we used in situ hybridization analysis to show that FGFR3 also has a unique pattern of expression during organogenesis. Like FGFR1 and FGFR2, FGFR3 was expressed in the germinal epithelium of the neural tube (9.5-16.5 days pc). However, at 1 day postpartum and in the adult brain, FGFR3 was expressed diffusely and localized in cells with morphologic characteristics of glia, a pattern distinctly different from the discrete neuronal expression of FGFR1. FGFR3 was also expressed at high levels in differentiating hair cells of the cochlear duct, but was not detected in other sensory epithelia. Outside the nervous system, the highest level of FGFR3 expression was found in the cartilage rudiments of developing bone. During endochondral ossification, FGFR3 was expressed exclusively in resting cartilage, a pattern distinct from FGFR1 and FGFR2 which are also expressed during this process. Unlike FGFR1 and FGFR2, FGFR3 was not detected in most other epithelial or mesenchymal tissues during these stages of organogenesis. The unique expression pattern of FGFR3 compared with the other FGF receptors strongly suggests that FGFR3 performs specific functions during organogenesis.